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FILE - In this Oct. 16, 2011, photo, former Marine Capt. Timothy Kudo sits outside his apartment in the Brooklyn borough of New York. Kudo walks among civilians carrying a burden of guilt most Americans don’t want to share. A veteran of the wars in Iraq and Afghanistan, Kudo thinks of himself as a killer. "I can't forgive myself ... and the people who can forgive me are dead," he says. Over this decade's wars, there’s been an unprecedented explosion of study into warzone psychology and an evolving understanding of post-traumatic stress disorder. (AP Photo/John Minchillo)

FILE - In this Oct. 16, 2011, photo, former Marine Capt. Timothy Kudo sits outside his apartment in the Brooklyn borough of New York. Kudo walks among civilians carrying a burden of guilt most Americans don’t want to share. A veteran of the wars in Iraq and Afghanistan, Kudo thinks of himself as a killer. "I can't forgive myself ... and the people who can forgive me are dead," he says. Over this decade's wars, there’s been an unprecedented explosion of study into warzone psychology and an evolving understanding of post-traumatic stress disorder. (AP Photo/John Minchillo)